This invention relates to the field of application techniques for flowable material. More particularly, this invention relates to an improved exhaust flow control in a photoresist application system.
One of the central and recurring processes by which integrated circuits are formed is that of applying a coating of photosensitive material (typically called photoresist) to the substrate on which the integrated circuits are formed, patterning and developing the photosensitive material, and then selectively processing the underlying portions of the integrated circuits exposed in the patterned portions of the layer of photosensitive material. This series of process steps is repeated over and over again, with many different variations, during the process of fabricating the integrated circuits. Therefore, any problem with the photolithography processing of the substrates tends to have dramatic and far reaching effect on the cost of the manufacturing process and the integrity of the integrated circuits produced.
Traditionally, substrates are coated with the layer of photoresist using a photoresist application system. A photoresist application system optionally includes a number of components to apply and set the photoresist layer to the substrate. A photoresist dispenser dispenses the photoresist onto the top surface of the substrate. After the desired amount of photoresist is dispensed onto the substrate, a chuck holding the substrate is ramped up according to a predetermined acceleration profile to one or more predetermined rotational rates. The acceleration and rotation of the substrate causes the photoresist to spread across the surface of the substrate. Excess photoresist is shed from the substrate at it spreads out to the edges of the substrate, and then off of the edges of the substrate.
The excess photoresist that is spun off of the substrate enters a cup that is disposed around the substrate, and which is a part of an exhaust system. The exhaust system uses an exhaust stream of gas, typically ambient air, to help drawn the excess photoresist down through the exhaust system and away from the substrate to a collection point, such as a sump. The flow of the exhaust stream helps to reduce a blow back of the excess photoresist back onto the substrate. When blow back occurs, the effected areas of the substrate do not expose or develop properly and the substrate must be reworked or the quality of the integrated circuits underlying the effected areas tends to be compromised. Thus, the exhaust stream plays a relatively important role in ensuring that the photoresist coating process proceeds in a proper manner.
As generally indicated above, the excess photoresist has a tendency to blow back onto the substrate if the pressure differential of the exhaust stream through the exhaust system becomes positive. Therefore, it is desirable for the exhaust stream pressure to decrease along the length of the exhaust system. However, even when there is a gradual decrease in pressure along the length of the exhaust system, various temporary and spurious conditions can cause droplets of photoresist to blow back onto the substrate.
Thus, there is a need for a system and a method for applying photoresist to a substrate that reduces blow back of the entrained portion of the excess amount of the flowable material from a downstream position in the exhaust system to the substrate.
The above and other needs are provided by a method of applying a layer of a flowable material to a substrate. The substrate is received with a rotatable chuck, and an amount of the flowable material is dispensed on to the substrate. The substrate is spun on the rotatable chuck, thereby spreading the flowable material across the substrate and conveying a surplus amount of the flowable material away from the substrate. An exhaust stream is created with a vacuum source. At least a portion of the surplus amount of the flowable material conveyed away from the substrate is entrained into the exhaust stream, which exhaust stream is conveyed into an exhaust system. A pressure drop is created in the exhaust stream across a vane anemometer within the exhaust system. The blow back of the entrained portion of the surplus amount of the flowable material from a downstream position in the exhaust system to the substrate is thereby reduced.
Thus, positioning the vane anemometer in the exhaust system tends to create a sudden and distinct pressure drop across the vane anemometer, which tends to reduce the occurrence of blow back of the flowable material from the portion of the exhaust system that is downstream from the vane anemometer, and which is at a relatively lower pressure, to the portion of the exhaust system that is upstream from the vane anemometer, and which is at a relatively higher pressure, and which is where the substrate is processed.
In various preferred embodiments, the flowable material is photoresist, the substrate is a semiconductor wafer, and the rotatable chuck and the exhaust system are components of a photoresist application system. The external surface of the vanes of the vane anemometer are preferably made of a material that is resistant to the adherence of the flowable material. Most preferably, the vane anemometer has magnets in the tips of the vanes, and the rotational rate of the vane anemometer is detected with sensors located outside of the exhaust system, which sensors detect the magnets located within the vanes of the vane anemometer.
In an especially preferred embodiment, a signal corresponding to the velocity of the exhaust stream in the exhaust system is produced and reported. An alarm condition is signaled when the velocity of the exhaust stream in the exhaust system is less than a set point velocity. In other embodiments the application of the flowable material to additional substrates is prohibited when the velocity of the exhaust stream in the exhaust system is less than the set point velocity.
In an apparatus for applying a layer of the flowable material to the substrate, a rotatable chuck receives the substrate, and a dispensing unit dispenses an amount of the flowable material onto the substrate, The rotatable chuck rotates the substrate and thereby spreads the flowable material across the substrate, and conveys a surplus amount of the flowable material away from the substrate. An exhaust system receives the surplus amount of the flowable material. A vacuum source creates an exhaust stream within the exhaust system, and the exhaust stream entrains at least a portion of the surplus amount of the flowable material conveyed away from the substrate and received by the exhaust system. A vane anemometer disposed within the exhaust system creates a pressure drop in the exhaust stream across the vane anemometer within the exhaust system, and thereby reduces blow back of the entrained portion of the surplus amount of the flowable material from a downstream position in the exhaust system to the substrate.